1. Thermodynamic Stability of Li4Ti5O12 for Use at Anodes of
Lithium Ion Batteries
Deniz Cetin1, Keping Hua2, and Srikanth Gopalan1,2
1Division of Materials Science and Engineering, Boston University, 15 Saint Mary’s Street, Brookline, MA 02446
2Department of Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA 02215
Abstract
Experimental
Conclusions
Formation of solid electrolyte interphase (SEI) increases the cell internal
impedance and reduces the charge rates in lithium ion batteries (LIB) and
causes significant cell performance limitations. Lithium titanate, Li4Ti5O10 ,
(LTO) is a promising lithium storage material for anodes that does not form SEI,
but it suffers from poor charge and discharge rates which arise from low
lithium ion and electron conductivity at operation temperatures.
In order to improve the performance of the LIB anode, ionic and electronic
conductivities should be enhanced. We present in this work to test the stability
of LTO in molten salt media. In this work, materials will be synthesized at
temperatures higher than 800°C by solid state reaction and their
thermodynamic stabilities will be investigated in molten salt media.
Future Work
Reaction mechanism involves:
1)Dissolution of constituents 2)Reaction of the constituents in solution
3)Precipitation of final compounds upon exceeding solubility limit
Method
Transport through molten salts is typically orders of magnitude faster compared to
solid-state diffusion. Thus, the kinetics of reactions in a molten salt mixture are also
orders of magnitude faster compared to solid-state processes, and this facilitates the
synthesis of various compounds. Reverse reactions are also expected to be rapid in
molten salt media. That is, if a given compound is thermodynamically unstable, its
decomposition into constituent oxides is expected to be equally rapid in molten salts.
Single Phase Material
(High T Calcination)
molten salt
air
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Precursors
molten salt
air
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The precursors of LTO, that are lithium
carbonate and titanium dioxide, are reacted
in LiCl-KCl molten salt media for 8h at
450°C. Shown on the left is the XRD
pattern of the final product after washing
away the molten salt media. Peaks of
Li2TiO3 and the excess TiO2 are present in
the final product.
Figure2: XRD pattern of the final product after molten salt exposure of the precursors.
Precursors, lithium carbonate and titanium dioxide, do not readily form LTO at
temperatures lower than 600⁰C. In a molten salt medium maintained at
temperatures higher than 600⁰C, synthesis of LTO may be faster than solid
state reaction.
• Formation of LTO will be repeated at temperatures higher than 600⁰C.
References
I, Veljković, Poleti D, Karanović Lj, Zdujić M, and Branković G. 2011. Solid state synthesis of extra phase-pure
Li4Ti5O12 spinel. Science of Sintering 43, (3): 343-351
Discussion
Veljković et al. defines the following reaction mechanism for formation of LTO from its
precursors of lithium carbonate, Li2CO3, and titanium dioxide, TiO2.
According to the reaction mechanism shown above, formation of an intermediate
product, Li2TiO3, occurs between 400-600 ⁰C before forming LTO from its precursors.
Since the molten salt experiment is being performed at around 400⁰C, about 30⁰C
above the LiCl-KCl eutectic temperature, obtaining this intermediate product as a
result of the molten salt test is expected.
Figure1:: Schematic of the possible results of the molten salt experiment.